More Matrices, More Problems…or Maybe Not?

In the clinical research industry, you deal with a plethora of different and dirty matrices that all need to be cleaned up before being injected into your instrument. Whether it be urine, serum, whole blood, or oral fluid, all of these matrices contain different interferences that need to be removed by proper sample preparation. The problem is that preparing your samples before analysis can be tedious, time consuming, and difficult. While analytes of interest are going to influence what type of sample prep technique you select, what if we were to evaluate the specific interferences that need to be removed from different matrices needs first? Let’s look at a couple common matrices that need some sample prep help.

Urine: The Average Joe. Urine is utilized in clinical research because it is easy to get results with minimal sample preparation, however, the sample collection method can be difficult and sometimes lead to false negatives or false positives. Most scientists perform an enzyme hydrolysis using β-Glucuronidase on their urine samples to break the glucuronide bond that forms during drug metabolism. To avoid shooting a large protein onto their LC column and ruining the column’s lifetime, they can dilute their sample down, about a 10x dilution, and “shoot” or inject it into their column, which is common but doesn’t eliminate the protein. Performing proper sample preparation, such as Solid Phase Extraction (SPE), Supported Liquid Extraction (SLE) or β-Gone (a specialized β-Glucuronidase Removal Product) will ensure that the enzyme will be eliminated. This leads to longer column lifetimes, greater analyte sensitivity, and a possible reduction in instrument maintenance. All three are viable options for labs who need to eliminate β-glucuronidase before analysis.

Whole Blood/Plasma: Old Faithful. Whole blood is always going to be around in clinical and toxicology research because it provides accurate results and is a good determination of what is being transported around the body. Problems usually arise due to the invasive collection techniques (count me out for getting my blood drawn!) and extensive sample preparation that must occur. Whole blood must be broken down by plasma, red blood cells, and white bloods, which all take a lengthy amount of time. Protein precipitation, phospholipid removal, and SPE are all acceptable options for a whole blood matrix clean-up.

Oral Fluid: The New Kid on the Block. This has been an emerging matrix that has gained popularity for its simple sample collection and a precise detection directly after drug use. Oral fluid samples can be quickly obtained by an individual, which is why it is gaining rapid acceptance within the testing marketplace. An immense challenge occurs during the transportation of the oral fluid, due to the oral fluid device’s buffer solution that contains surfactants, which negatively impact LC-MS results by causing ion suppression. SPE is a viable option for labs that are working with oral fluid that need to clean-up the surfactants from their matrices. Two different SPE methods can be utilized depending on your analytes of interest: one method utilizes a single SPE cartridge for a quick and easy oral fluid clean-up and a double SPE cartridge method is the ultimate matrix clean-up to ensure samples are ready for injection onto the mass spec.

Whatever diverse matrix you are working with in the clinical and toxicology research—whole blood, urine, or oral fluid—the focus should be to make sure that negative matrix effects are eliminated and ensuring that proper isolation of analytes occurs. After cleaning up the matrix, analytes of interest can be considered to be the best sample prep technique. This can be done through a multitude of different options starting from simple protein precipitation to cleaner and more complex methods such as SPE.